To unlock this achievement/trophy, every character in the game needs to be unlocked. All but one character will be unlocked through campaign mode. Gargoyle will be the only chacter left. To unlock him you need to reach level 22 in online play or simply complete both red sides by completing the campaign on both Black and White side. If you decide to go this route, beware that the unlock will occur at the end-results screen.
Atlas is an action-rpg with rogue-like elements where you use your ability to control the ground to fight the enemies and move through procedurally generated worlds.
